WALTHAM – Police say a 9-year-boy was killed and his mother seriously injured when a pizza delivery vehicle crashed into their SUV at a Waltham intersection.

The boy, whose name was not immediately released, was ejected from the vehicle and taken to Newton-Wellesley Hospital after the crash at about 4:45 p.m. on Wednesday where he was pronounced dead. His mother was flown to a Boston hospital with a serious leg injury. A 1-year-old girl in the vehicle was treated as a precaution.

Police say the 19-year-old driver of the other vehicle had just finished delivering a pizza and may have run a stop sign. He was not hurt. His name was not released and no charges were immediately filed.